Hey those are some nice pics! I'll d-load them and add them to my site. I'm going to try to get in touch with my source either this week or next (you know who you are! ) to see if I can get some more rounds to confirm the measurements. Hate to base the chamber reamer off of only one example...

Once I get a couple more rounds to confirm the size, I'm going to see about setting up the lathe to make a reamer. I have three (oil quench) O1 steel rods ready to go!

I can do everything EXCEPT the reamer flutes. If I only knew someone who had a parting head on their mill!

With the SP-6, I wonder if it sheds the jacket in a fluid substance, sort of like a hollowpoint, but instead of expanding, the jacket just peels off...

Reportedly, the SP6 was designed after the previous AP rounds were ruining barrels due to the lack of soft metals in the bore. The result was the SP6's thin lead "jacket" around the smaller steel core.

I don't think the jacket would separate as you describe. Once through the bore, it would be swaged tighter due to the rifling. One would think that would make the jacket more prone to stay with the core.